title: Swept-frequency feedback interferometry using terahertz frequency QCLs: a method for imaging and materials analysis.
abstract: The terahertz (THz) frequency quantum cascade laser (QCL) is a compact source of high-power radiation with a narrow intrinsic linewidth. As such, THz QCLs are extremely promising sources for applications including high-resolution spectroscopy, heterodyne detection, and coherent imaging. We exploit the remarkable phase-stability of THz QCLs to create a coherent swept-frequency delayed self-homodyning method for both imaging and materials analysis, using laser feedback interferometry. Using our scheme we obtain amplitude-like and phase-like images with minimal signal processing. We determine the physical relationship between the operating parameters of the laser under feedback and the complex refractive index of the target and demonstrate that this coherent detection method enables extraction of complex refractive indices with high accuracy. This establishes an ultimately compact and easy-to-implement THz imaging and materials analysis system, in which the local oscillator, mixer, and detector are all combined into a single laser.
authors.forename: Aleksandar D
authors.initials: AD
authors.lastname: Rakić
authors.forename: Thomas
authors.initials: T
authors.lastname: Taimre
authors.forename: Karl
authors.initials: K
authors.lastname: Bertling
authors.forename: Yah Leng
authors.initials: YL
authors.lastname: Lim
authors.forename: Paul
authors.initials: P
authors.lastname: Dean
authors.forename: Dragan
authors.initials: D
authors.lastname: Indjin
authors.forename: Zoran
authors.initials: Z
authors.lastname: Ikonić
authors.forename: Paul
authors.initials: P
authors.lastname: Harrison
authors.forename: Alexander
authors.initials: A
authors.lastname: Valavanis
authors.forename: Suraj P
authors.initials: SP
authors.lastname: Khanna
authors.forename: Mohammad
authors.initials: M
authors.lastname: Lachab
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Wilson
authors.forename: Edmund H
authors.initials: EH
authors.lastname: Linfield
authors.forename: A Giles
authors.initials: AG
authors.lastname: Davies